Based on a study that David Ullman did on VGs for the top of the Velocity, specifically to generate better airflow into the cooling NACA ducts, I’ve decided to replicate his experiences. He determined that larger vortex generators that are typically used on airfoils would be required to get into the high energy air at the edge of the boundary layer in this location. He calculated, and then validated on his airplane, that the VGs needed to be approximately 2″ tall and 15″ ahead of the NACA to improve the cooling flow.

Here is David’s study (link and  PDF).

That indicated the VG should be about 2.5″ long, 2″ high, and separated by 5″. So I laided up some triax with 2 layers of BID to give me a good piece of stock 10″ long to cut out 4 VGs from. After I made the shapes I put a template on the roof for a trial run. We flew a test course at 25 squared, came in and shutdown. I then used duct tape to secure the VGs, and we went out and flew the same course and power settings. This showed about 15 degrees cooler temps across the board, and maybe better than that at lower speeds where we’ve historically had difficultly getting cooling air into the engine.

Since I was only mounting these temporarily, I didn’t locate them with the exactness really needed, so next I’ll create a template with the exact angles and distances in paper, and use that to silicone the VGs in their final locations after I paint them.

Creating VG stock

Setting up for temporary placement

VGs taped down

Placement Template



15″ ahead of Naca

Posted By: Brett Ferrell
Tuesday October 14th, 2014 at 1:13 PM

Categories: Cooling Flight Testing NACA and Cooling Plenum
Tags: Building Cooling Fuselage NACA VG

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